Violence again marred preparations for the Democratic Republic of Congo's constitutional referendum, with three voting offices in Kinshasa being attacked by explosive devices early Saturday morning. Elsewhere across the country, voting material was still being dispatched at the last minute, campaigning for the "yes" and "no" campaigns stopped and observers prepared for the beginning of what the U.N. says is the most difficult electoral process it has been involved in.

Three schools in Kinshasa being used as voting stations for Congo's constitutional referendum were attacked early Saturday, highlighting the potential for violence in Sunday's poll.

U.N. sources said an explosion destroyed one station for several hundred voters while Molotov cocktails thrown at two others would not disrupt the poll, which will be held to decide whether to accept Congo's post-war constitution.

The referendum is the first step in a series of elections meant to draw a line under years of war and bring democracy to the Congo, a mineral rich country at the heart of Africa that has endured decades of dictatorship and chaos.

Congo's last war, a five-year conflict that drew in six neighboring countries, was described as Africa's World War and has killed nearly four million people since 1998, mostly from hunger and disease.

Campaigning for "no" and "yes" votes ended late Friday. Mobile phone companies sent out mass text messages encouraging Congolese to vote in large numbers. And observers deployed across the vast country, which is the size of Western Europe.

With the collapse of the most basic infrastructure, elections officials and material have to be airlifted into remote bush towns, ferried in dug out canoes down streams and carried by head through the thick jungle.

The lack of infrastructure, coupled with a vast potential electorate of some 25 million people and continued fighting in much of the east, the United Nations says Congo's electoral process is the most difficult and complicated it has been.

A "yes" vote paves the way for local, parliamentary and presidential elections, which must be held by mid-2006.

A "no" vote means the document will have to be re-drafted and the electoral process delayed, something the international community, which has invested billions of dollars in the peace process, would like to avoid.